Pump



United rates PUMP Ludwig T. Stoyke and Oliver W. Scheflow, Rockford, 111.,

assignors to Sundstrand Machine Tool Co., a corporation of Illinois Application August 14, 1253, Serial No. 374,252

3 Claims. (Cl. 103-126) This invention relates to a gear pump and more particularly to a gear pump consnucted and arranged as to operate under extreme pressure conditions.

It is the general object of this invention to produce a new and improved gear pump.

It is a more specific object of this invention to produce a gear pump in which noise, erosion and other undesirable characteristics caused by cavitation are substantially completely eliminated.

Another object of the invention is to produce a gear pump provided with means for insuring complete filling of the gear spaces preceding the outlet port of the pump before oil in said gear spaces is subjected to the full extent of outlet port pressure thus reducing cavitation and cavitation erosion to an insignificant factor.

Another object of the invention is to produce a gear pump provided with means for gradually introducing oil substantially under outlet port pressure into partially void gear spaces preceding the outlet port so that the pressure andvolume of oil inthe gear spaces is gradually increased as the oil is broughtto outlet port pressure.

Yet'another object of the invention, is to produce a crescent type gear pump in which a portion of the crescent ,or end cap is beveled away to form a passage along the surface of'the crescent, said passage being connected with the outlet'port and being of a design for providing gear spacespreceding the outlet port with a gradually decreasing volume of oil under substantially outlet port pressure, the maximum volume being introduced at a point where the gear spaces are at substantially the greatest distance from the outlet port and still sealed from the inlet port, saidgvolume decreasing thereafter as the gear spaces are gradually filled.

T Other and further objects of this invention will be apparent from the following description and drawings which Fig. 1 is a vertical section through an oil pump embodying the invention;

Fig; 2 is a vertical section along line 2--2 of Fig. 1; and Fig. 3 is a section taken'substantially along line 33 of Fig. 2. Y

While this invention is susceptible of embodiments in .manydifferent forms, there is shown in the drawings and will herein be described in detail one specific embodiment, .with the understanding that the present disclosure is to be considered as an exemplification of the principles of the .invention and is not intended to limit the invention to the 2,774,309 Patented Dec. 18, 1956 2 embodiment illustrated. The scope of the invention will be pointed out in the appended claims.

In the form of the pump chosen for the purposes of disclosure, there is provided a two part casing 10, 10', a crescent type gear pump 11, a drive shaft 12, a mechanical seal 13 for the drive shaft, and a strainer 14. It is con: templated that the shaft 12 will be connected by suitable means to a driving motor (not shown), that an inlet port 15 will be connected to a source of oil supply.

The casing parts are formed to provide a chamber 16 in which the pumping device 11 and the strainer 14' are located. The part 10 is in the form of a closure or cover and is bolted to the part 10 by means of a plurality of screw devcies 17.

The pumping device ll comprises an externally toothed pinion gear 18 and an internally toothed ring gear 19 meshing with the pinion, a crescent guard element 20, and a housing for these members consisting of a cylindrical block 21 with a cut away cylindrical chamber 22 therein, said chamber being positioned eccentrically of the center of said block and being of a depth equal to the thickness of the gear, pinion and crescent which are housed in said chamber. The end plate 23 is used as a closure for the pumping unit. A plurality of screw devices 23a secure the end plate to the block 21 and the block to the casing 10.

The pinion is mounted centrally with respect to block 21 and eccentrically with respect to'the center of the chamber 22 and is secured to the drive shaft 12 by means of the pin 24. The crescent member 20 fits snugly between the spaced or separated portions of the gear and pinion and is secured to the block 21 by means of the pins 24a. The end plate 23 is provided with an inlet passage (not shown) which opens at one end to the chamber 16 r and at the other end to the inlet port 26 of the pump which is located at one 'end 25 of the crescent. Preferably, an arcuate cavity 26a is formed in block 21 opposite the inlet port so as to facilitate filling of the gear spaces in the gear and pinion. An outlet port 27 is formed'in the block 21 adjacent the other end 28 of the crescent and an arcuate cavity 27:: is associated therewith, and means in the form of an outlet passage 29 are connected to the outlet port. p i I The crescent member 20 is of substantially the same thickness as the gear and pinion. One surface 30 of the crescent is bevelled to provide a passage 31 along said surface, said passage being deepest at its beginning near the center of the surface at point 32, the portion of said bevelled surface most remote from the outlet port. The bevelled surface tapers gradually from point 32 toward the outlet'port and terminates at point 33 where the outlet port end of the crescent is substantially the same thickness as the gear and pinion so that there is no seepage of oil from the outlet port over said crescent end. A pas sageway 34 opens in the surface of said passage near the area of maximum depth thereof and communicates with a passageway 35 to allow a flow of oil under substantially outlet port pressure into said passage. A plug in one end 36 of the passageway 35 prevents the escape of oil from said end. The end plate 23, gear 19, pinion l8, crescent 20 and block 21'are machined to close tolerances and positioned to permit substantially no leakage of oil except through the passage 31.

It is a general purpose of the passage herein disclosed to provide means for insuring complete filling of the gear spaces preceding the outlet port of the pump before. oil in said gear spaces is subjected to the full extent of outlet port pressure and to thereby substantially reduce noise, cavitation erosion and other undesirable characteristics caused by cavitation, v

The deleterious effects of cavitation on gear pumps be pheric pressures existing at high altitudes.

low inlet pressure at high altitudestheoil suppliedto the gear spaces by the-inletport frequently containsa good a 3 come particularly pronounced in gear pumps utilized under extreme pressure conditions such as the low atmos- Because of deal of undissolved air and oil vapor and may even be in the form of foam so that gear spaces after filling by'the inl'etiport contain air and oil vapor bubbles entrained with the oil, the air and oil vapor having come out of solution because of low pressure conditions. The void' space instantaneous effect of the high pressure is to' violently force the gaseous bubbles in the oil back into solution, thereby'causing the said bubbles'to implode and to drive oil :particlestraveling at extremely high velocities against 7 par-ts of the pump with eroding'effect,

Thepositioningand 'design of the passagemeans disclosed hereinfor insuring substantially complete filling 'of the g ar Spaces and substantially complete reduction of cavitation and the efiects thereof is important.

The passa e 31 is formed to supply oil under elevated pressure in a decreasing volume to a plurality of gear 7 spaces preceding the outlet port27 and thus said passage has a volume-decreasing toward the outlet port from point 32 of maximum depth to point 33 adjacent the outlet port. -A decreasing volume of oil is supplied to the gear spaces to conform with the. rated filling of the void spaces therein; that is, as each, gear space is gradually filledbyoilunder elevated pressure, the volume of void spacex'thereingradually decreases and consequently the passage is designed to supply a decreasing volume of oil under-"elevated; pressure in relation to the need therefor or the decrease in void space.

Initial communication by the passage with a gear space occurs at a point 32 of maximum passage volume when a gearspace isat' substantially the greatest distance from the outlet: portyet still, sealed from theinlet-port after being filled thereby. At this pointthe volume of void space in each gear space is the greatest and saidgear space is, at said point,;-subjected to an initial maximum volume .of oil under elevated pressure, said volumegradually decreasing as the gear space. gradually fills and the void volume 'graduallyidecreases as the gear. space passes along the decreasing volume of the passage. toward the outlet PQI i The length of the bevelled surface or'passage may be determined by the sealing efiect whichis desired for the pinion gear'and' hence thelength of the passage may be outlet port. In pumps having output flow of from 5 to .10 7 gallons per minute, the preferred depth of the passage is approximately .015 to .025 inch. a

The depthof the passage and'its taper "are a function .of certain :known conditions such asinletvpressure, speed, capacity and discharge pressure and therefore must'be varied when any of the combination 'of conditions are changed. A specific sized passage, however, will generally accommodate 3.20 percent variation in oil flow.

the depth and taper of the passage must vary as the volume of void spaces decreases or increases vwith a change in combination of conditions as aforestated.

Upon rotation of the shaft 12 the gear spaces passing from the outlet port and still sealed from the inletport. Due to the design and positioning of said passage, said gear spaces are subjected to a gradually decreasing volume of oil under substantially outlet port pressure, said 7 oil under elevated pressure serving to insure complete filling of the gear spaces prior to the discharge of the oil therein into the ou'tletport and to gradually increase the oil pressure in said gear spaces so as to gradually collapse gaseous bubbles which may be entrained in the oil; thus forcing gas in said gear spaces substantially back into solution priof't'o the point where. oil in said j gear spaces is subjected to the full extent of outlet port pressure. The gradual forcing of the gas back into solution and'the smooth transition of the oil in the gear spaces from, inlet pressure to the full extent of outlet port pres sure is accompanied by practically no noise, vibration,

cavitation 'erosionor other undesirable characteristics caused by cavitation.

Weclaim: I c

l. A gear pump comprising, a casing having acylindrical pumping chamber with inlet and outlet ports, an internal ring gear rotatably mounted in the chamber, a pinion of the same thickness as and meshing with, said ring gear, a shaft supported eccentrically of saidchamber and carrying said pinion gear, said pinion gear having an external diameter less than the internal diameter of-the ring gear to providean arcuate space therebetween, a member of substantially the same thickness as the gear and pinion fixed in said chamber and located in said space, said mem- 7 member having a bevelled portion extending from side to give the member substantially the shape of a crescent with a The maximum depth of the passage and its taper are i also afunction of the volume of void spaces existing in the gear-"spaces afterifilling by the inlet port, and therefore side of said member along one surface thereof'beginning nearthe center of said surface and terminating short of the outlet end of said member to provide a passage sealed from said outlet port and defined between said member and said plate, said bevelled portion increasing in depth from adjacent saidoutlet end to saidbeginning whereby i said passage gradually decreases-in'volume fromlits be' ginning toward the outlet port, a passageway connecting said passage with the outlet port, said passage establishing communication between the outletpoi-t and a plurality of. gear spaces in the ring' and pinion gears immediately pre ceding the outlet port to introduce into said gear: spaces a; gradually decreasing volume of oil at substantially outa let port pressure. p 7 '2. A gear pump comprisingpa casing havingja cylindrical pumping chamber 'with'inlet and outlet ports,- an

internal ring gear rotatably mounted in the chamber, a V pinion of thesame thickness as and meshing with said ring gear andcarried on a shaft supported'eccentricall'y of said chamber, said pinion having an external diameter less than 7 I the internal diai'neter of thering gear to provide an arcuate space therebetween, a member of the same, thickness as the geariandpinion fixed in saidchamber'and located in said space, said member bein tapered at each and to said ends'being located adjacent the inlet and outlet ports of the chamber, a 'plate closing one end of the chaniber and contacting onejsurface of theg'ear'and pinioniandef the'me'mber in a sealing relationship; said member having a bevelled portion amn a sur'faeeth i'eof extending from side toside of said member end-beginning intermediate the ends of said surface and terminating short of the outlet port end of said member to provide a passage sealed from said outlet port and defined between said member and said plate, said passage having a maximum depth at its beginning of approximately .015 to .025 inch and progressively decreasing to zero depth adjacent the outlet port whereby said passage decreases in volume from its beginning to adjacent the outlet port, passageway means connecting said passage with the outlet port, said passage communicating in decreasing volume with a plurality of gear spaces in the ring and pinion gears immediately preceding the outlet port to subject oil in said gear spaces to a gradually decreasing volume of oil substantially at outlet port pressure as oil in the gear spaces is brought to outlet port pressure with rotation of the gear and pinion.

3. A gear pump comprising a casing having a pumping chamber provided with inlet and outlet ports, a gear rotatably supported in the chamber, a second gear of the same thickness as the first gear and mounted to have a portion meshing with said first gear and a portion spaced therefrom, a member having a portion of the same thickness as the gears fixed in said chamber adjacent the outlet port and between the spaced portions of said gears in substantially a sealing relationship with said gears, means defining a passage in said chamber along a surface of said member and opening to gear spaces on both sides of the 25 6 member, said passage being shaped to have a volume gradually decreasing toward said outlet port and being in communication with'a plurality of gear spaces immediately preceding said outlet port, and a passageway formed in the casing independent of said surface and opening at one end to the outlet port and at its other end to said passage remote from the outlet port, whereby to subject oil in said gear spaces to a gradually decreasing volume of oil at substantially outlet port pressure as the gear spaces approach said outlet port with rotation of said gears.

References Cited in the file of this patent V UNITED STATES PATENTS 1,689,587 Holmes Oct. 20, 1928 2,159,720 Wahlmark May 23, 1939 2,232,983 Wahlmark Feb. 25, 1941 2,309,683 Wahlmark Feb. 2, 1943 2,544,144 Ellis Mar. 6, 1951 2,630,759 Mahlon Mar. 10, 1953 2,684,637 Erikson July 27, 1954 FOREIGN PATENTS 325,849 Germany Sept. 21, 1920 331,054 Great Britain July 3, 1930 

